I wonder if people mean 'seductive' like the place charms you, about Paris, when they call it sinister and demonic? I mean it does have a reputation for a romantic / sexual vibe, maybe some people like more 'jolly' and simple places.
But yes, the poster on prev page (sorry should hae copied your name) - some people aer not open to something unfamiliar and see it as uncomfortable maybe, mind you it's their right, so they can choose elsewhere.
I loved Ile St Louis in Paris, it's magical, and yes sort of exciting. Not a huge fan of the very centre around the Opera, Concorde etc - it's just grand, and I prefer charming .